a) Field of the Invention:
This invention relates to an optical isolator and, more particularly, to a polarization-independent type optical isolator capable of functioning without consideration for a plane of polarization of incident light.
b) Description of the Prior Art:
FIG. 1 shows an example of the arrangement of a conventional optical isolator. This optical isolator is such that after incident light passes through a first polarizer 1, the plane of polarization of the incident light is rotated at angle of 45.degree. by a Faraday rotator 2 and the incident light further passes through a second polarizer 3 which has the plane of polarization inclined at 45.degree. with respect to the first polarizer. For return light reflected in a direction opposite to the incident light, on the other hand, only a component of the light which coincides in plane of polarization with the second polarizer 3 traverses the second polarizer 3 and then the plane of polarization thereof is further rotated at 45.degree. by the Faraday rotator 2. It follows from this that the reflected return light which has traversed the Faraday rotator is such that the plane of polarization is rotated at 90.degree. with respect to the first polarizer 1, and thereby the reflected return light cannot reach the entrance side of the incident light. Hence, according to the conventional optical isolator, the reflected return light in the opposite direction is blocked and the function of the optical isolator of this type is thus performed. Also, if the isolator of the arrangement depicted in FIG. 1 is constructed in a plural, a higher effect of isolation can be brought about.
With such a conventional optical isolator, however, there has been the problem that since it is required that the plane of polarization of the first polarizer 1 is kept to coincide with that of the incident light, the function cannot be effectively performed in a light transmission system such that in particular the plane of polarization cannot be specified.